Non-Flammable Succinonitrile-Based Deep Eutectic Electrolyte for Intrinsically Safe High-Voltage Sodium-Ion Batteries

Intrinsically safe sodium-ion batteries (SIBs) are considered a promising candidate for large-scale energy storage systems. However, the high flammability of conventional electrolytes may pose serious safety threats and even explosions. Herein, we propose a strategy of constructing a deep eutectic electrolyte (DEE) to boost the safety and electrochemical performance of succinonitrile (SN)-based electrolyte. The strong hydrogen bond between S = O of 1,3,2-dioxathiolane-2,2-dioxide (DTD) and the α-H of SN endows the enhanced safety and compatibility of SN with Lewis bases. Meanwhile, the DTD participates in the inner Na+ sheath and weakens the coordination number of SN. The unique solvation configuration promotes the formation of robust gradient inorganic-rich electrode-electrolyte interphase, and merits stable cycling of half cells in a wide temperature range, with a capacity retention of 82.8% after 800 cycles (25 °C) and 86.3% after 100 cycles (60 °C). Correspondingly, the full cells deliver tremendous improvement in cycling stability and rate performance. This article is protected by copyright. All rights reserved.

Organosulfide-Based Deep Eutectic Electrolyte for Lithium Batteries

Deep eutectic electrolytes (DEEs) are a new class of electrolytes with unique properties. However, the intermolecular interactions of DEEs are mostly dominated by Li⋅⋅⋅O interactions, limiting the diversity of chemical space and material constituents. Herein, we report a new class of DEEs induced by Li⋅⋅⋅N interactions between 2,2'-dipyridyl disulfide (DpyDS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The strong ion-dipole interaction triggers the deep eutectic phenomenon, thus liberating the Li⁺ from LiTFSI and endowing the DEEs with promising ionic conductivity. These DEEs show admirable intrinsic safety, which cannot be ignited by flame. The DEE at the molar ratio of DpyDS:LiTFSI=4:1 (abbreviated as DEE-4:1) is electrochemically stable between 2.1 and 4.0 V vs. Li/Li⁺ , and exhibits an ionic conductivity of 1.5×10^-4  S cm^-1 at 50 °C. The Li/LiFePO₄ half cell with DEE-4:1 can provide a reversible capacity of 130 mAh g^-1 and Coulombic efficiency above 98 % at 50 °C.